Measuring conductivity of proton conductive membranes in the ...
Measuring conductivity of proton conductive membranes in the ... Measuring conductivity of proton conductive membranes in the ...
Measuring conductivity of proton conductive membranes in the direction of thickness However, it is highly likely that treatments the membrane undergoes in the manufacturing and processing processes, such as stretching and hot-press, will change not only its crystalline structure and dimensional stability in the longitudinal, transverse, and thickness directions but also exert some influence on its proton conductivity. There is a high probability of anisotropy3) in the proton conductivity of the membrane. On the other hand, PFSA membranes are being used in the direction of thickness for the solid polymer electrolyte fuel cells, and an anisotropically conductive membrane that was newly-developed must also be evaluated in various directions. Therefore, a reliable measuring technique with high stability, reproducibility and accuracy is required to evaluate proton conductivity in the direction of thickness of the membrane. The research for this report focuses on developing a stable and precise method of measuring conductivity in the direction of thickness for the proton-conductive polymer electrolyte membrane. 4) Measurements in the direction of thickness can be conducted with 2-probe *4 and 4-probe methods, but measuring with two probes is much easier than with four, and results are more stable as there are fewer inconsistencies with multiple specimens. This report presents the results obtained using the 2-probe method for conductivity measurements of ion exchange membranes. 2 Experimental method 2-1 Equipment and materials Table 1 lists the equipment and materials used in this research. Table 1 Equipment and materials Equipment/materials Manufacturer Impedance gain/phase analyzer - 13 - Model/registered product name Solartron Instruments SI 1260 Electrochemical interface Solartron Instruments SI 1287 Temperature & humidity chamber Ion exchange membrane ESPEC Corporation PL-1KPH E. I. du Pont de Nemours and Company Nafion ® 117 Espec Technology Report No20
Measuring conductivity of proton conductive membranes in the direction of thickness 2-2 Specimen preparation MEA specimens were made by hot-pressing electrodes to a Nafion ® 117 membrane. In a preliminary test, measurements were made with two kinds of MEAs. One type of MEA specimen was produced by hot-pressing two Pt foil electrodes, coated with Nafion ® solution on one side each, to a membrane. The other MEA specimen was produced by hot-pressing two Pt foil electrodes to a membrane without using the Nafion ® coatings. Results showed good reproducibility with the Nafion ® -coated specimen, therefore, in this report specimens were prepared by coating a Nafion ® solution onto one surface of the electrodes for voltage impression unless otherwise specified. For 2-probe measurements in the direction of thickness, specimens were prepared by hot-pressing a Nafion ® membrane sandwiched into electrodes consisting of two pieces of metal sheets (5 mm x 5 mm x 10 to 20µm) or carbon papers (5 mm x 5 mm x 190µm) situated opposite each other. On one face of the metal sheets, a coating was applied with 5 µl of 5 wt. % Nafion ® dispersion solution in lower aliphatic alcohols followed by vacuum drying one hour at room temperature. No coating was used on the carbon paper electrodes. Photo 1 shows the configuration of the membrane/electrode assembly (MEA *5 ) used in this report for the 2-probe measurements in the direction of thickness. The assembly is made of platinized Pt black sheets and Nafion ® 117 membrane. Photo.1 MEA of Pt black/Nafion ® 117 for 2-probe measurements in the direction of thickness For 4-probe measurements in the direction of thickness, the specimens were prepared by sandwiching and hot-pressing platinum wire electrodes between three Nafion ® membranes and then, as with the specimens for the 2-probe measurements, hot-pressing metal sheets that had been coated with Nafion ® solution and vacuum-dried onto both outside faces of the assembly. - 14 - Espec Technology Report No20
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<strong>Measur<strong>in</strong>g</strong> <strong>conductivity</strong> <strong>of</strong> <strong>proton</strong> <strong>conductive</strong> <strong>membranes</strong> <strong>in</strong> <strong>the</strong> direction <strong>of</strong> thickness<br />
2-2 Specimen preparation<br />
MEA specimens were made by hot-press<strong>in</strong>g electrodes to a Nafion ® 117 membrane. In a<br />
prelim<strong>in</strong>ary test, measurements were made with two k<strong>in</strong>ds <strong>of</strong> MEAs. One type <strong>of</strong> MEA<br />
specimen was produced by hot-press<strong>in</strong>g two Pt foil electrodes, coated with Nafion ®<br />
solution on one side each, to a membrane. The o<strong>the</strong>r MEA specimen was produced by<br />
hot-press<strong>in</strong>g two Pt foil electrodes to a membrane without us<strong>in</strong>g <strong>the</strong> Nafion ® coat<strong>in</strong>gs.<br />
Results showed good reproducibility with <strong>the</strong> Nafion ® -coated specimen, <strong>the</strong>refore, <strong>in</strong> this<br />
report specimens were prepared by coat<strong>in</strong>g a Nafion ® solution onto one surface <strong>of</strong> <strong>the</strong><br />
electrodes for voltage impression unless o<strong>the</strong>rwise specified.<br />
For 2-probe measurements <strong>in</strong> <strong>the</strong> direction <strong>of</strong> thickness, specimens were prepared by<br />
hot-press<strong>in</strong>g a Nafion ® membrane sandwiched <strong>in</strong>to electrodes consist<strong>in</strong>g <strong>of</strong> two pieces <strong>of</strong><br />
metal sheets (5 mm x 5 mm x 10 to 20µm) or carbon papers (5 mm x 5 mm x 190µm)<br />
situated opposite each o<strong>the</strong>r. On one face <strong>of</strong> <strong>the</strong> metal sheets, a coat<strong>in</strong>g was applied with<br />
5 µl <strong>of</strong> 5 wt. % Nafion ® dispersion solution <strong>in</strong> lower aliphatic alcohols followed by vacuum<br />
dry<strong>in</strong>g one hour at room temperature. No coat<strong>in</strong>g was used on <strong>the</strong> carbon paper<br />
electrodes. Photo 1 shows <strong>the</strong> configuration <strong>of</strong> <strong>the</strong> membrane/electrode assembly<br />
(MEA *5 ) used <strong>in</strong> this report for <strong>the</strong> 2-probe measurements <strong>in</strong> <strong>the</strong> direction <strong>of</strong> thickness.<br />
The assembly is made <strong>of</strong> plat<strong>in</strong>ized Pt black sheets and Nafion ® 117 membrane.<br />
Photo.1 MEA <strong>of</strong> Pt black/Nafion ® 117 for 2-probe measurements <strong>in</strong><br />
<strong>the</strong> direction <strong>of</strong> thickness<br />
For 4-probe measurements <strong>in</strong> <strong>the</strong> direction <strong>of</strong> thickness, <strong>the</strong> specimens were prepared<br />
by sandwich<strong>in</strong>g and hot-press<strong>in</strong>g plat<strong>in</strong>um wire electrodes between three Nafion ®<br />
<strong>membranes</strong> and <strong>the</strong>n, as with <strong>the</strong> specimens for <strong>the</strong> 2-probe measurements,<br />
hot-press<strong>in</strong>g metal sheets that had been coated with Nafion ® solution and vacuum-dried<br />
onto both outside faces <strong>of</strong> <strong>the</strong> assembly.<br />
- 14 -<br />
Espec Technology Report No20
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